1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus and a process cartridge as well as an electrophotographic photoreceptor used for copiers and printers using coherent light as the light sources.
2. Discussion of the Background
Recently, a printer having a laser diode as the light source is widely used because of its compactness, high reliability, high-speed printing and high image quality. However, a photoreceptor which is sensitive to infrared light is desired because the laser diode has a wavelength of from 780 to 830 nm. As such photoreceptors, inorganic photoreceptors formed from cadmium sulfide doped with copper, indium, etc. and from selenium including increased tellurium have been used. However, organic photoreceptors are prevailing recently in view of the low pollution high productivity, stable quality and low cost. Among the organic photoreceptors, particularly a functionally-separated multilayer photoreceptor having a charge generation layer and a charge transport layer attracts attention in view of the high sensitivity and high durability because the materials can be flexibly selected.
The charge generation layer of the multilayer photoreceptor generates a charge by absorbing light, and the thickness of the layer is typically 0.01 to 5 xcexcm for shortening the carrying range of the photo-carrier to prevent the recombination and the trap thereof.
In addition, a charge transport layer which scarcely absorbs imagewise light is typically used in view of the sensitivity.
Generally, the light volume which is absorbed in the photosensitive layer has a limit. The imagewise light coming in the photosensitive layer is not all absorbed therein, and some of the light reach the substrate and reflect on the surface thereof. The reflected light comes in the photosensitive layer again, and interferes with the imagewise light and the light reflecting on the surface of the photosensitive layer. Such a phenomenon remarkably occurs when the imagewise light is a coherent laser beam, causing image-density irregularity when a solid image and a half tone image are produced.
In order to prevent such a light interference, there is a method, in which an intermediate layer, including a resin containing a dispersed pigment having a large refraction index and an average particle diameter of from about 0.2 xcexcm to 5 xcexcm, is formed between the substrate and the photosensitive layer to scatter the light and prevent the mirror reflection. However, such an intermediate layer cannot completely prevent the light interference when the imagewise light volume and the developing condition change, and when a minimization of the diameter of the imagewise light and a high-density writing are desired for a higher image quality
On the other hand, a non-cut aluminium tube is considered instead of a conventional cut aluminium tube recently in view of the manufacturing cost and the adherence to the photosensitive layer. However, the non-cut aluminium tube has a surface having a high smoothness and a high reflectance, and has the opposite effect to the light interference.
Accordingly, an object of the present invention is to provide an electrophotographic image forming apparatus preventing the image-density irregularity due to the light interference.
Briefly this object and other objects of the present invention as hereinafter will become more readily apparent can be attained by an image forming apparatus including at least an image irradiator configured to irradiate a photoreceptor with a coherent light beam while scanning to form pixel light spots thereon for forming an electrostatic latent image thereon, wherein the light spots overlap with adjacent light spots; and an image developer configured to develop the electrostatic latent image with a developer, wherein the photoreceptor comprises an intermediate layer located overlying an electroconductive substrate, a charge generation layer located overlying the intermediate layer and a charge transport layer located overlying the charge generation layer, wherein the charge generation layer satisfies the following relationship:
T1xe2x89xa63.5% 
wherein T1 represents a relative mirror reflectance of the charge generation layer against the coherent light beam when the coherent light beam irradiates the charge generation layer formed on the intermediate layer at an incident angle of 5xc2x0.
These and other objects, features and advantages of the present invention will become apparent upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.